The present invention relates to releasable interlock assemblies, particularly to those used in medical devices such as catheter introducer assemblies, catheter introducer-to-accessory assemblies, and catheters which generally comprise two or more portions, each of which must releasably engage with the other. The present invention relates particularly to elective engagements where the axial engagement between the portions must withstand forces urging the portions to separate from one another.
Catheter introducers provide a reusable conduit for the passage of guide wires, catheters, pacemaker leads, or other medical devices, e.g. biopsy instruments, through the skin, flesh, and vessel walls to gain access into blood vessels or other body passageways and cavities. Many types of accessories are used in conjunction with catheter introducers, such as hemostasis valves, Tuohy-Borst adapters, and aseptic catheter shields These accessories must by necessity couple to the catheter introducer or each other, or both, in some combination. This invention is directed to providing a simple and secure means of releasably coupling any combination of these and other devices to one another.
In typical use, say for introducing a catheter into a blood vessel, a physician inserts a needle through the body flesh and into a blood vessel, and then inserts a guide wire in to the blood vessel through the center passage of the needle. The needle is then removed leaving the guide wire in place. The introducer assembly is then inserted over the guide ire such that the tapered distal portion of the dilator acts to gradually expand the puncture opening to ease the pas sage of the introducer sheath into the blood vessel. After the introducer sheath has been inserted to a desired depth within the blood vessel, the dilator portion is removed from within the introducer portion. In this disclosure, xe2x80x9cproximalxe2x80x9d refers to the portions of an introducer nearest to the physician or health care worker performing the insertion procedure, and xe2x80x9cdistalxe2x80x9d refers to the portions of the introducer nearest to, or inside of, the human or animal patient receiving the catheter.
During the initial insertion of the introducer assembly, the body""s resistance to the expansion of the puncture opening exerts forces on the distal portion of the dilator tending to push the dilator distal end rearwardly in the proximal direction into the introducer sheath. In order to ensure that the tapered distal portion of the dilator remains extended beyond the blunt distal end of the introducer sheath during the initial insertion the introducer assembly, the dilator hub should be connected to the introducer hub to prevent relative axial movement of the two portions. It is important that the dilator hub and the introducer hub not disengage during the insertion procedure, but be capable of being disengaged when desired.
Catheter introducers of various forms exist in the prior art. Such devices generally consist of: (1) a dilator comprised of an elongated flexible tube with a hub permanently affixed to the proximal end. The distal end of the tube is fashioned into a generally conical tapered tip. (2) an introducer comprised of an elongated flexible tube or sheath with a hub permanently affixed to the proximal end and a distal tip which is fashioned in such a way as to minimize the resistance to insertion and trauma to the body tissue. The introducer interior diameter is sized to slidably accommodate the exterior of the dilator tube, since the two are inserted into the body as a set.
As a set, the dilator resides within the introducer, and while assembled, the distal tip of the introducer resides axially proximal to the proximal end of the tapered end of the dilator. As the name would suggest, the purpose of the dilator is to dilate or enlarge a hole in the body tissues so as to allow entry of the tubular portion of the introducer. This dilation is accomplished by means of the conical tip of the dilator which, as it is progressively inserted into the body, stretches the tissue radially outward to allow entry of the distal portion of the introducer. Once the insertion is achieved, the dilator is removed and the introducer remains as a transcutaneous conduit whereby other instruments are afforded ready access into the passageway.
During the insertion process, the body tissues resist stretching, and the resistance force vector in the axial direction would cause the dilator to move axially relative to the introducer if there were no means present to prevent such relative movement. Accidental movement of the dilator relative to the introducer during the insertion process is undesirable, for if the distal tip of the introducer is allowed to extend beyond the proximal end of the dilator tip, significant trauma to the vessel and surrounding tissues would result.
Numerous means for releasably connecting the introducer to the dilator, or to connect accessories to the introducer, or to one another, are known in the prior art. Prior art means for releasably connecting the dilator hub and the introducer hub have utilized rotatably engaging studs and complimentary slots, tapered fits, exterior clips, and ring and collar mechanisms. Many of these devices either require a significant effort to engage the locking mechanism, or do not prevent the portions from accidentally disengaging, or leave exposed protrusions on one or more members which can snag and tear a surgical glove.
The present invention solves the problems associated with prior art devices by generally providing an axial coupling means with an improved rotatably engaging releasable interlock between the dilator and introducer portions of an introducer assembly. It reduces the risk of inadvertent disengagement while minimizing the effort required for proper deployment and eliminates externally protruding portions. Additionally, all protrusions, grooves, and parts of the locking mechanism are internal when the releasable interlock is engaged, thus eliminating the risk that such parts could snag and tear a surgical glove.
The present invention describes an improvement of a rotatably engaging axial coupling connection between at least two constituents of a medical device, such as between a dilator hub and an introducer hub of a catheter introducer, although the scope of application of this invention is not limited to the example.
The releasable interlock assembly with axial and rotational engagement has a first portion having a generally cylindrical or conical male member at the engaging end with one or more radially disposed grooves which engage a second portion. The second portion has a generally cylindrical or conical female member at the engaging end dimensioned so as to receive the male member of the first portion. The female portion has one or more protrusions which extend from the interior wall of the tapered female member, or socket, radially inward towards the common longitudinal axis of the two portions and which engage and cooperate with the grooves of the first portion. Upon axial engagement of the two portions, male member into female member, one portion is rotated relative to the other portion causing the protrusions in the second portion to enter engagement with the grooves of the first portion. Upon continued rotation, the protrusions of the second portion encounter a dimensional interference with the grooves of the first portion. Upon continued rotation, and with a greater amount of applied torque required, one or both of the portions elastically deform into a stressed condition so as to overcome the dimensional interference thus allowing continued relative rotational motion between the two portions.
With continued applied torque, this relative rotational motion is sustained, with one or both portions in a stressed condition, until the inwardly radially directed protrusions of the second portion come to a blind end of the grooves of the first portion at which point the dimensional interference between the two portions is significantly reduced. This represents the releasably locked state of engagement between the two portions. The sudden reduction of dimensional interference and subsequent stress relaxation provides a tactile sensation thus signaling the user that the releasably locked state has been achieved. Only by reversing the amount and direction of applied torque and retracing the original path of the protrusions within the grooves can the interference fit be defeated and disengagement of the two members achieved.
The preferred embodiment of this invention achieves the engagement and disengagement within a ninety-degree range of rotation. The preferred embodiment of this invention would be comprised of portions with generally elastic, but resilient, materials which will elastically deform at the strain represented by the interference fit overcome, but would possess a relatively high stiffness and natural frequency of vibration so as to spring back into their unstressed state with a minimum of damping. Some of the suitable materials would be polypropylene or acrylonitril butadine styrene (ABS), or metals having these characteristics.